Combustion turbines comprise a casing or cylinder for housing a compressor section, combustion section and turbine section. The compressor section comprises an inlet end and a discharge end. The combustion section comprises an inlet end and a combustor transition. The combustor transition is proximate the discharge end of the combustion section and comprises a wall which defines a flow channel which directs the working gas into the turbine section.
A supply of air is compressed in the compressor section and directed into the combustion section. The compressed air enters the combustion inlet and is mixed with fuel. The air/fuel mixture is then combusted to produce high temperature and high pressure gas. This working gas is then ejected past the combustor transition and injected into the turbine section to run the turbine.
The turbine section comprises rows of vanes which direct the working gas to the airfoil portions of the turbine blades. The working gas flows through the turbine section causing the turbine blades to rotate, thereby turning the rotor, which is connected to a generator for producing electricity.
As those skilled in the art are aware, the maximum power output of a gas turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is feasible. The hot gas, however, heats the various turbine components, such as the transition, vanes and ring segments, that it passes when flowing through the turbine. Such components are critical components because their failure has direct impact on the operation and efficiency of the turbine.
Accordingly, the ability to increase the combustion firing temperature is limited by the ability of the critical components to withstand increased temperatures. Consequently, various cooling methods have been developed to cool turbine hot parts. These methods include open-loop air cooling techniques and closed-loop cooling systems.
Conventional open-loop air cooling techniques divert air from the compressor to the combustor transition to cool the turbine hot parts. The cooling air extracts heat from the turbine components and then transfers into the turbine's flow path where it merges with the working gas of the turbine.
Conventional turbine closed-loop cooling assemblies receive cooling fluid, either air or steam, from a source outside the turbine and distribute the cooling fluid circumferentially about the turbine casing. Unlike open-loop cooling systems, the closed-loop cooling fluid typically flows through a series of internal cooling passages of a critical component, while remaining separated from the working gas that flows through the turbine. After cooling the critical component, the cooling fluid is diverted through channels to a location outside the turbine.
Thermal Barrier Coatings (TBCs) are commonly used to protect critical components from premature breakdown due to increased temperatures to which the components are exposed. Previously, TBCs were used solely to extend the life of critical components by reducing the rate of metal waste (through spalling) by oxidation.
At present, in Advanced Turbine Systems (ATSs), however, the operating characteristics are such that the survivability of the TBC on blades and vanes is critical to the continuing operation of the turbine. Essentially, the high temperature demands of ATS operation and the limits of their state-of-the-art materials make the presence of the TBCs critical to the continued life of the underlying critical components. Failure of the TBC results in failure to meet design requirements and engine failure. It is, therefore, desirable to provide a system that would monitor the level of TBCs on critical components of a combustion turbine to signal when a critical component begins to overheat.
Critical components can also overheat for reasons other than due to TBC erosion, such as blocked cooling passages, cooling chamber failures or cooling media supply failures. It is, therefore, desirable to provide a system that would determine when a critical component begins to overheat.
Monitoring the condition of a TBC in the hostile environment of an operating combustion turbine is not easy. Because TBCs generally fail by spalling at or close to the coating/ceramic layer interface, coating degradation can be only indirectly observed from the external surfaces of a blade or vane. It is, therefore, desirable to provide a monitoring system that utilizes remote sensing.
There are particular challenges attendant to monitoring turbine vanes. The vanes are stationary, but are numerous. Typically, in an ATS, there are at least 30 vanes in a vane row. Therefore, multiple or distributed sensors must be employed to properly monitor each vane. The use of multiple sensors, however, would be expensive, unless inexpensive sensors were used, which would not perform well under such adverse environmental conditions found in an operating turbine. It is, therefore, desirable to provide a monitoring system that would be both cost effective and relatively inexpensive.